The present invention relates to a semiconductor type gas rate sensor which is capable of electrically detecting a deflection of a gas flow in a gas path when an angular velocity acts on the sensor body and, more particularly, to a semiconductor type gas rate sensor whose body is made of semiconductor substrates.
A conventional gas rate sensor is ordinarily designed to force gas through a nozzle port into a gas path toward a pair of heat wires (heat-sensitive resistance elements) arranged on the right and the left of the gas path, to sense a change of differential resistance in the paired heat wires, which is produced when the gas flow is deflected to the left or the right by the action of an angular velocity applied to the sensor body, and to produce a detection signal corresponding to the differential output of the paired heat wires, by which a direction and a value of the angular velocity acting on the sensor body can be determined.
In Japanese Laid-Open Patent Publication No. 3-29858 there is disclosed a miniature semiconductor type gas rate sensor whose body has a gas path and a pair of heat-wires arranged therein and is manufactured by semiconductor micro-machining on the basis of IC technology.
As shown in FIGS. 3 to 5, the body of the semiconductor type gas rate sensor is constructed in such a way that a lower semiconductor substrate 1' having a half nozzle port 31 and a half groove 41 etched thereon and an upper semiconductor substrate 2' having a half nozzle port 31 and a half groove 41 etched thereon are bonded to each other so as to precisely couple the half ports 31 and the half grooves 41 to form a nozzle port 3' and a gas path 4' in the assembled body.
The lower semiconductor substrate 1' has a bridge portion 6 formed across the gas path 4' and a pair of heat wires 51 and 52 formed by patterning on the etch-formed bridge portion 6. In FIG. 1, electrodes 7 are formed at the outside end of each heat wire by patterning.
To make the gas rate sensor having the thus constructed body be sensitive enough to accurately detect an angular velocity acting on its body, it is necessary to realize an optimal flow of gas formed through a nozzle port 3' into the gas path 4' in the sensor body to satisfy various conditions which will be described later. In this connection, it is increasingly important to select a suitable form and size of the sensor body. In other words, the size and form of the gas rate sensor have not been sufficiently considered to this day with the viewpoint of attaining the optimal conditions of a flow of gas forced into the gas path in the sensor body through the nozzle port.